Reproduction of images from printed surfaces



May 26, 1970 w. P. TAYLOR 3,514,305

REPRODUCTION OF IMAGES FROM PRINTED SURFACES Filed oct. 2o, 195s ggz/iam P7 Zm fw im United States Patent O 3,514,305 REPRODUCTION OF IMAGES FROM PRINTED SURFACES William P. Taylor, Hamilton, Ohio, assignor to U.S. Plywood-Champion Papers Inc., a corporation of New York Filed Oct. 20, 1965, Ser. No. 498,821 lint. Cl. B44c 3/00; B65d 75/30 U.S. Cl. 1l7--1.7 37 Claims ABSTRACT F THE DISCLOSURE The reproduction of images from printed surfaces, such as printed paper, by placing a moistened copy sheet against the printed surface to reproduce the image on the copy sheet. The reproduction of images can be effected in the absence of special heat and light. A packaged moistened copy sheet ready for use by merely removing it from its package and placing it in contact with a printed document to reproduce the printed sheet image in the copy sheet. A copy sheet image is formed either as a latent developable image or as a permanently visible image and in either instance, can be transferred to a iinal sheet to produce a right reading image.

This invention relates to the reproduction of images, or, more particularly, to the making of copies from a printed surface by placing a copy sheet against the printed surface to effect the reproduction of the image on the copy sheet.

The invention is directed to a new concept in copying by which an image on a printed sheet may be reproduced on a copy sheet simply by holding the copy sheet on the printed sheet for a few seconds without any special application of electricity, heat, light, or the like. The invention employs the discovery that when the moisture contents of the printed and copy sheets are different7 moisture vapor will migrate from one sheet to the other to a greater extent in the non-image areas than in the image areas. This selective migration is due in part to the fact that printing ink or the physical change in the structure of the sheet produced by the printing process which establishes the image areas provides a barrier to the migration of vapor at the image areas.

In the preferred form of the invention, the concept is employed in the following way. An extremely thin film is formed on one surface of an impermeable plastic copy sheet. The film is porous in that it is capable of retaining moisture as by adsorption. The lm is moistened and is held against a printed cellulosic sheet (a page of a book, for example) for a few seconds to permit the moisture to vaporize and to diffuse toward the cellulosic printed sheet. The comparatively high absorptive quality of the cellulosic non-printed areas of the printed sheet effects a dry ing out of the adjacent moistened surface of the copy sheet while leaving those areas overlying the printed images in a more moist condition. The image is thus reproduced on a copy sheet in the form of relatively moist areas. In that form it is not always immediately useful. Other -steps will be described hereafter for fixing a discernible image in the copy sheet or a final sheet to which the copy sheet is applied, but, in all of these, the basic mechanism of image reproduction through selective vapor migration is used.

There are `many techniques which may be employed for obtaining a fixed discernible image. There are three principal categories of techniques which will be described herein and designated selective dissolution, developer, and image transfer. Each of these has its variants, and, in some instances, the steps of one category of process are ICC used in carrying out the steps of another category of process. All of the processes have in common the selective migration in the image and non-image areas of vapor between a copy sheet and a printed sheet.

In one of the more practical forms of the invention, a porous film is formed on an impermeable copy sheet, and that film is moistened with a liquid which is entirely of predominantly water. The moistened film of the copy sheet is placed against a printed cellulosic paper and the water vaporizes and selectively migrates toward the non-image areas. The water vaporizes over the image areas, but, because of the vapor barrier created by the printing, a substantial equilibrium is almost immediately achieved, and the film overlying the image areas remains moist. At the non-image areas, the avidity of the cellulose in the paper for water effects the rapid and continuous extraction of the vapor from the space between the sheets. Thus, there is a continual drying out of the copy sheet film in the non-image areas while the areas overlying the image areas remain relatively moist.

As stated above, the invention is a vapor diffusion process. There are many processes in the prior art in which reference is made to diffusion of a dye or the like from one sheet to another, but these are liquid diffusion processes involving a capillary iiow. The vapor diffusion character of the present process has been determined by interposing a nylon mesh between the printed sheet and the copy sheet to preclude capillary migration of the liquid between the sheets. This system produced a discernible image on the copy sheet.

The invention is principally useful in reproducing images from cellulosic papers, including those cellulosic papers which have been coated with a pigment and binder, because such papers constitute the greatest source Of printed material from which reproductions would be made and because of the great capacity of cellulose t0 absorb moisture. The invention is not necessarily limited to such papers, however, for as long as a sheet has disparate avidity for moisture, as between the printed and non-printed areas, the invention is applicable to such a sheet. Further, the most practical use of the invention involves the migration of water vapor from a copy Sheet to a printed sheet, but the invention is not necessarily so limited. For example, the process of the invention may be performed by applying ammonia to a printed sheet and placing diazo copy paper against the printed sheet. The ammonia vapors diffuse to the diazo copy paper most rapidly in the non-image areas and thereby form blue, mirror images on the copy paper, thereby demonstrating the applicability of the invention to vapors other than water and that the invention embraces the migration of vapors from the printed sheet to the copy sheet.

DEFINITIONS Throughout this description and claims, the following terms will be used with the definitions set forth.

Printed sheetwany surface bearing an image to be reproduced in which there is a disparate avidity for vapors as between the image and non-image areas, usually by virtue of the printing ink forming a pattern which is relatively impervious to vapors.

Copy sheet-the sheet placed against the printed sheet and onto which a mirror image of the printed sheet is reproduced. Usually the copy sheet is constituted by an impermeable base sheet on which a porous film is formed.

Impermeable-as applied to the base sheet of the copy sheet, having that quality of preventing any appreciable amount of the liquids or vapors involved to migrate into or out of the sheet in the time required to make a copy.

Final sheet-a sheet against which the copy sheet is placed to form a permanent right-reading image.

Porous film-a very thin film formed on one surface of the copy sheet. The film is discontinuous and is therefore capable of retaining, as by adsorption, a small quantity of moisture uniformly distributed over the area of the sheet. The film may be formed by coating the copy sheet or by etching the copy sheet in any suitable manner.

Moist (moisture, moistening)-pertaining to that small amount of liquid on the surface of a sheet (usually the copy sheet) used in the process as, for example, the amount left on a porous film when the film is wetted, wiped dry with an absorbent paper towel, and dried for a few seconds. The liquid is usually water or a mixture of water and one or more additional constituents, but may be any liquid or mixture of liquids which are capable of selective vapor migration with respect to a printed page.

Mixture of liquids-an intimate and homogenous association of liquids regardless of whether one liquid is dissolved in another.

Solvent-as used in relation to the selective dissolution process and certain variants of the transfer process, any liquid capable when sufficiently concentrated of softening a porous lm to permit its coalescence, but which is less avidly absorbed by the unprinted areas of a printed sheet than some or all of the other constituetns of the moisture used in the process. Usually the solvent is mixed with Water and is less avidly absorbed by cellulosic fibers.

Paper-a sheet formed of natural cellulose or synthetic fibers whether or not tub sized, whether or not lled or coated, and whether or not parchmentized. If coated, the coating must not form an impermeable barrier to the diffusion of vapor.

It has been an objective of the invention to provide a process of reproducing an image from a printed sheet onto a copy sheet comprising the steps of creating a greater moisture content in one of said sheets, placing said copy sheet on said printed sheet for a sufficient length of time to permit said moisture to diffuse from the wetter sheet to the drier sheet selectively to the greatest extent in the unprinted areas.

It has been another objective of the invention to provide a process of reproducing copies from a printed sheet whose image areas have an avidity for vapors different from the non-image areas comprising the steps 0f forming on an impermeable copy sheet a thin film caable of having its optical properties changed by the presence of a solvent, moistening said film with a mixture of an inert liquid and said solvent, the concentration of said solvent in said inert liquid being too weak to effect a change in the optical properties of said film, said printed sheet having a greater avidity for said inert liquid than said solvent, placing said sheet with said film against said printed sheet until substantial vapor diffuses from said film toward the non-image areas of said printed sheet, and separating said sheets.

It has been another objective of the invention to provide a process of reproducing an image from a printed sheet of cellulosic fibers whose image areas are printed with an ink which forms a barrier to the migration of vapor comprising the steps of forming a thin porous film on a surface of an impermeable copy sheet, moistening said film with water or water and a reacting chemical, placing said copy sheet on said printed sheet for a sufficient length of time for the water vapor of said moistened film selectively to diffuse from the film to the non-image areas of said printed sheet, and subjecting said sheet to a developing medium which reacts in the presence of water or water and the reacting chemical to produce a color in the image areas of said copy sheet.

Another objective of the invention has been to provide a process for reproducing an image from a printed sheet comprising the steps of using the vapor diffusion technique described above to produce a moisturized image area on a copy sheet and thereafter to transfer that image to a final sheet.

These and other objectives of the invention will become more readily apparent from the following description taken in conjunction with the drawings in which:

FIG. 1 is a perspective view of a package of copy sheets formed in accordance with one embodiment of the invention, and

FIG. 2 is an enlarged cross sectional view taken along lines 2 2 of FIG. l.

SELECTIVE DISSOLUTION PROCESS One of the objectives of the invention has been to provide the simplest possible system, from an operating and material standpoint, for making reproductions of a printed page. To this end, the selective dissolution process has been developed. In accordance with the process, the user places a specially prepared copy sheet against the printed sheet for a few seconds and a permanent readable image appears on the copy sheet. Nothing more is required.

The copy sheet is prepared by forming an extremely thin opaque porous film on one surface of an impermeable transparent sheet. The film is moistened with a sensitizing liquid comprising a mixture of water and an organic solvent, the concentration of the solvent being too weak to dissolve and thus change the optical properties of the opaque film. The copy sheet is held against the printed sheet to be reproduced for a few seconds. In the non-image areas the water vapor which migrates toward the printed sheet is rapidly absorbed in the cellulosic fibers. The solvent vapor is not so rapidly absorbed because the cellulosic bers have a greater avidity for water than for the solvent. Thus, the film overlying the non-image areas is selectively robbed of its water content, thereby increasing the concentration of the solvent to the extent that it solvates and changes the optical properties of the film. The change in optical properies is usually a transparentizing of the film in the non-image areas, the film being rendered transparent by the action of the solvent which sol-vates and thereby permits the collapsing and coalescing of the discontinuous opacifying particles by which the film is formed. In the lmage areas, the barrier created by the printing prevents mlgration of either the water or solvent vapor away from the porous film and the concentration of solvent remains too weak to solvate the lm. The net effect is to transparentize the film in the non-image areas and to maintain the film opaque in the printed areas. The image areas can be viewed as right-reading areas through the reverse side of the transparent sheet.

When the desired reproduction has been attained, the copy sheet is removed from the printed sheet and permitted to dry in air. The vapor pressures or rates of evaporation of the solvent and water respectively are such that during the air drying of the sensitizing liquid, the concentration of the solvent in the image areas never reaches the level which would permit it to transparentize the film.

EXAMPLE 1 A cellulose acetate sheet was dipped in acetic acid for about 4 seconds and rinsed with water and dried. This treatment produced a cellulose acetate copy sheet with an opaque, porous film. Under microscope, the surface of the opaque sheet appeared as a porous, fibrous cotton batting or the like.

The opacified cellulose acetate copy sheet was then sensitized by dipping in a 25% by volume solution of 1,4- dioxane in water for about 4 seconds. The excess liquid was then blotted ofi the surface of the sheet by pressing between the absorbent paper towels so that no free liquid was detectable by sight or touch. The sheet was permitted to dry by exposing it to air for a few seconds to insure the absence of free liquid on its surface. The resulting surface of the cellulose acetate sheet contained dioxane-water moisture. The sheet was then held in uniform contact with a printed sheet of paper for about 15 seconds, after which it was removed from the printed paper and exposed to air until the residual moisture evaporated. A white, permanent image against a relatively transparent background developed on the surface of the sheet upon exposure to air. The permanent image on the surface of the copy sheet was a mirror image of the printed matter on the paper. When viewed from the side of the cellulose acetate copy sheet opposite the imaged surface, a positive right reading image appeared on the relatively transparent background.

EXAMPLE 2 The procedures described in Example 1 were repeated with the same materials, only in this example a nylon fabric of stocking mesh and double thickness was interposed between the surface of the cellulose acetate copy sheet and the printed sheet of paper during the 15 second Contact period. A permanent image was produced on the surface of the copy sheet and `was of the same character as described in Example 1.

EXAMPLE 3 A cellulose acetate sheet was dipped in a mixture of one part by volume of isopropanol, two parts by volume glacial acetic acid and one part by volume of water for 5 seconds. The sheet was then rinsed in water for 25 seconds and then the excess liquid was blotted off with damp paper towels. The moist surface of the cellulose acetate copy sheet was then held in uniform contact with a printed sheet of paper about 1/2 minute. After removal of the copy sheet from the printed paper and exposure to air, a white, permanent mirror image developed against a transparent background on the surface of the sheet.

TABLE I.-EXAMPLES OF SELECTIVE DISSOLUTION SYSTEMS Copy Sheet Ex. Base Sheet Porous Film 4 Cellulose Acctate. Cellulose Acetate e Scnsltizer Solution (percent by volume) 11% Butyrolactonc,

22% Ethylene gylcol monocthyl ether, 67% water.

5. .do do.D 11% Dioxancl 22% Ethylene glycol,' monoethyl ether, 67% water.

6 Glass Plate Ethyl Cellulose b-- 25% Ethylene glycol monoethyl ether 75% Water.

7 Polypopylone dol Scnsitizcr Solution ol' Example 6.

8v Polystyrcne do.b Do.

(i Polypropylene.. do. 20% lentoxoLm 80% water.

10 Saran do.n 11% Bntyrolactonc,

22% Ethylene glycol monoethyl other, 67% water.

1l do do.c 11% Dioxane. 22%

Ethylene glycol monoethyl ether, 67% water.

3% Glyccryl Triacetate, 3% Propylene Carbonate, 27% Ethylene glycol monoethyl ether, 07% water.

.-do.d.. Scnsitizer Solution of Example 12.

14. Polypropylene do.d Do.

Polystyrcnc Cellulose Nitrate e, 5% Propylenc Carbonate, 15% Ethylene glycol monoethyl ether, 15% Isopropanol, water.

16. Polypropylene .do.e Sensitizer solution of Example 15.

17 Polystyrcne .do. 8% Propylenc Carbonate, 24% lso propanol, 68% water.

18 Polypropylene do.e Sensitizer Solution oi Example 17.

19 Polystyrene (10.0 7% Pentoztonc,n 14% Ethylene glycol nionoethyl other, 79% Water.

20 Polypropylene do.e Scnsitizcr Solution oi Example 19.

2l, Polystyrcnc Cellulose Acetate 8% Propylenc Carbon- Butyrate-f ate, 24% lsoprcpanol, 68% water.

12 Glass Plate Cellulose Acctatad 13 Saran Polypropylcnc Cellulose Nitrate 15% Butyrolactone,

SANTOLITE Water.

23 do do 7% Pentoxone,n

14% Ethylene glycol monoethyl ether,

79% water. 24 do Polyvinyl 15% Butyrolactonc,

Acetate Poly 85% Water. (vinyl methyl ether-malais anhydride).h 25 do Potyvinyl 5% N-methyl-Z- Acetate.i pyrrolidone,

w er. 26. Polystyrene do.i 10% diacetone alcohol,

90% water. 2 Polypropylene...v Polyvinyl acetate 10% Ethylene glycol poly (vinylmonoethyl ether, methyl other 90% water. maleic anydride) Carbopol 934.1' 23 do (10.5 20% Dioxane, 80%

water. 2D, do Polyvlnyl Do,

Acetato polystyrene.k

Percent solutions are given as g. per ml. ol solution in the following footnotes:

e Formed in dippingr the cellulose acetate base sheet in acetic acid for a lcw seconds, rinsing with water and drying.

b Formed by coating the base sheet with about a 5% solution of ethyl cellulose iu methanol and drying.

U Formed by coating the base sheet with a 4.2% solution of ethyl gellnlosc in a solvent blend of methanol-heptane (4:1 volume ratio) and trying4 d Formed by coating the base sheet with a 2.5% solution of cellulose acetate in a solvent blend of acctonc-toluenc-cthylcne glycol monoethyl cthcr (2:1:1 volume ratio) and drying,

e Formed by coating.T the base sheet with an 8% solution of cellulose iitrate in a solvent blend of methanol-acetone (4:1 volume ratio) and rying.

f lorined by coatingT thc base sheet with a 5.3% solution of cellulose acetate-butyratc in a solvent lend of methanol-acetone (3:1 volume ratio) and drying.

14 Formed by coating the base sheet with a 7.5% solution of cellulose nitrato and a plasticiczr (cg. SANTOLITE M.H.P. which is a rcsinous condensation product of aryl sulfonamide and formaldehyde by Monsanto Chemical Company) (9:8 weight ratio) in a solvent blond of methanol-denatured alcohol (1:13 volume ratio) and drying.

h Formed by coating the base sheet with a 3.3% solution of polyvinyl acetato-poly (vinyl methyl ctl1er-malcic anhydride) (1:1 weight ratio) in acetone and drying.

i Formed by coating the basc sheet with a 2.5% solution of polyvinyl acct-att` in acetone and drying.

i Formed by coating the base sheet with a 2.5% solution of polyvinyl acetate-poly (vinyl methyl other-malato anhydride and a carboxy vinyl polymer of high moleculai- Weight (cg. Carbopol 934 by B. F. Goodrich Chemical Company) (1:30:0.7 weight ratio) in a solvent blend ol' acetonemethanol (6:1 volume ratio) and drying.

k Formed by coating thc base sheet with a 2.5% solution of polyvinyl acetato-polystyrene (3:1 Weight ratio) in acetone.

m Pentoxol is a commercial mixture of pcntanols by Shell Chemical Company.

n Pentoxone is a commercial mixture of pentanoncs by Shell Chemical Company.

EXAMPLE 30 (A) A glass plate was provided with a thin coating of a mixture of equal parts by weight of polyvinyl alcohol and poly (vinyl methyl ether-maleic anhydride). The coating was allowed to dry in air. The dried coating was then printed on with a grease pencil.

(B) A copy sheet was prepared by dip-coating one surface of a polypropylene sheet with a solution of 2 grams of polyvinyl acetate and 0.5 gram Ipoly (vinyl methyl ether-maeic anhydride) in 100 ml. of acetone and dried. The dried opaque, porous film was sensitized by dipping in a solution of 33% dimethyl sulfoxide in water, for about 10 seconds, and blotting off the excess liquid to render the surface moist with sensitizer.

The sensitized copy sheet was then held in uniform contact with the printed surface of the coated glass plate prepared in (A). After 30 seconds, the copy sheet was removed from the printed surface and a White permanent image was visible on the surface of the copy sheet. The image was of the same character as described in Example 1, but the transparent areas corresponded to the image areas of the glass plate.

(C) A glass plate was coated with a dispersion of 100 grams kaolin and 15 grams casein in 345 cc. water with suihcient ammonium hydroxide to disperse the casein,

eg., 2.25 grams of a 28% solution of ammonia, and dried. One part of dried surface-coated glass was written on with a grease pencil, a strip of aluminum foil was placed on a second part, and a third part was scratched through the coated surface, exposing bare glass.

A copy sheet which had been coated and sensitized as in (B) above was placed over the printed area, aluminum barrier area and scratched area of the coated glass for about one minute. Images of the printed area, the area made impervious to vapor by the aluminum and the scratched, intaglio relief area were all reproduced on the surface of the copy sheet. The images were permanent `and of the same character as that described for the image in Example 30(B).

In the Examples 30(B) and (C), the images formed were negatives because of the use of a slightly modified technique, and the mechanism causing the formation of negative images is believed to be as follows:

The sensitizer used was an aqueous solution of dimethyl sulfoxide, which evaporates slowly, and the film was sensitized by soaking in the solution, blotting off excess liquid, and allowing the film to dry for 1/2 to 1 minute before pressing it into contact with the printed page. This drying made it non-sticky and caused the surface to start to regain its original opacity. There was relatively concentrated solvent below this surface, ihowever, which was trying to diffuse back into the surface and evaporate, but was also dissolving slowly in the plastic as it became more concentrated. Where it was free to evaporate, it escaped along with the water, without causing any permanent change in opacity. Where it was blocked by any relatively impervious barrier, however (printing ink, grease pencil, glass, or aluminum foil) the organic solvent from the bulk of the coating replasticized the superficially-dried surface and caused the structure of the image areas to collapse and to become transparent.

In the disclosed examples, the copy sheet is treated with a sensitizing liquid prior to its application to the printed page. The application of the sensitizing fluid can be made by the producer of the copy sheet with the sheet being packaged in `a sealed container which will maintain the sheet in its sensitized condition and which will permit withdrawal of individual sheets for immediate copying application without substantial evaporation of the liquid from the remaining sheets. One such package is shown in FIGS. 1 and 2. The package indicated at 10 is a sealed pad of alternating plies of sensitized copy sheets 11 and sealing sheets 12 of a vapor impermeable plastic such as Saran. The copy sheets are, for example, a biaxially oriented plastic material having a thin porous film 13 on one surface thereof. The thin porous film is moistened with a sensitizing mixture, preferably of water and an organic solvent for the film. The sealing sheets 12 are longer and wider than the copy sheets so that they overhang the copy sheets all around the periphery of the package. The Saran sheets are heat sealed along their peripheral edges as at 14, thereby providing a seal for the package to prevent the escape of moisture from the sensitized sheets until they are ready for use. The manner of interleaving the copy sheets with impermeable plastic sheets which are sealed around their peripheral edges also creates individual sealed pockets 15 for respective copy sheets.

In use, the topmost package forming sheet 12 is stripped away from the overlying copy sheet and the copy sheet backed by the remaining package is immediately applied to the printed surface from which the copy is to be made. After a few seconds, the image is formed in the sensitized film 13 as described above, and the topmost copy sheet is removed from the package. The remaining copy sheets stay in a sealed condition in their respective pockets until ready for use.

Alternatively, the unsensitized but opacied copy sheets may be packaged in a dispenser having a dampening roller or the like over which the copy paper passes when dis- 8 pensed to moisten each copy sheet with the sensitizing fluid.

The copy sheet itself is preferably transparent so that a right reading image can be viewed from the surface opposite the sensitized surface. The sheet may be plastic, glass, or elastomeric material. It must be impermeable to the liquid with which its lm is moistened so that the liquid vapors lwill migrate away from the sheet rather than being absorbed into it. Its surface may be such as to have the capacity to be opacified by contact with a` solvent, followed by a water rinse, or, alternatively, an opacifying coating can be applied to the surface, the copy sheet merely forming a support for the opaque coating. Suitable materials for use as the copy sheet include glass, polyethylene, cellulose acetate, Saran, polystyrene (Trycite), polyester (Mylar), and polypropylene.

The opaque or porous surface film on the copy sheet may be constituted by lenses, prisms, scratches, bubbles, fibers, pits, crystals, beads, or the like. Preferably, the light scattering elements are between 0.2 and 0.35 micron in diameter and are separated by spaces of comparable magnitude, for such dimensions will provide optimum light scattering or opaciiication with respect to the visible spectrum. The surface film should be very thin, preferably less than one mil (0.001 inch) in thickness. The thickness of the iilm may have a preferred range of 0.01 mil to 0.5 mil. The film must be thick enough to retain sufiicient moisture for at least the period of time required to perform the steps of the process. That is, it must not become too dry during the time that it is being manipulated to apply it to the printed sheet and upon being applied to the printed sheet it must contain sufiicient moisture for carrying out the reaction or combining steps of the process. On the other hand, the film must not be so thick that it would contain enough moisture to cockle the printed sheet to which it is applied. Further, if the lm is too thick, the greater quantity of moisture in it tends to degenerate the sharpness of the image. The film must be capable of being solvated in suitable solvents in order to change its optical properties. Examples of suitable films include foamed or particulate cellulose acetate, cellulose nitrate, and vinyl chloride. As indicated, the surface film may be created by treating the base sheet with a suitable solvent, or, alternatively, the film may be formed by applyin g a coating directly to the sheet.

There are three principal criteria for the solvent. As the first criterion, the cellulosic fibers must have markedly less avidity for the solvent than for water with which the solvent is mixed. It is to be understood that in the preferred embodiment, water is used as the carrier with which the solvent is mixed for the reasons of its chemical inertness, its affinity to cellulosic fibers, and the obvious cost factor. The selection of another carrier having a disparate avidity to the cellulosie fibers as compared to the solvent would, of course, fall within the scope of the invention.

The second criterion is that the solvent must be capable of solvating or otherwise reacting with the opaque film to render it transparent or to change its character so that the portions of the film upon which it acts are easily discernible from the portions upon which there has been no activity. The solvent preferably should not have a strong odor, but, if it has an odor, the odor should be as inoffensive as possible. Operable solvents include butyrolactone, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether, dioxane, the pentanols, the pentanones, glyceryl triacetate and propylene carbonate (with a solubilizer such as alcohol or a glycol ether), propylene carbonate with a solubilizing agent such as alcohol or a glycol ether, isopropanol, ethanol, N-methyl-Z-pyrrolidone, acetic acid, tetrahydrofuran and the like.

As a third criterion, the solvent must have an evaporatio-n rate with respect to the water such that in drying in air the solvent never attains that concentration which would cause the image to disappear.

9 DEVELOPER EMBODIMENT The foregoing has been a description of what is considered to be a practical embodiment of this invention from the standpoint of simplicity and ease of operation. The following is a description of an alternative embodiment and variations thereof which result in entirely satisfactory reproductions from an aesthetic standpoint but which require a separate development step, usually involving a liquid developer. In the developer embodiment I employ the principle involved in selective diffusion embodiment, namely, that when a copy sheet is placed against a printed sheet and the two sheets have differing moisture contents, the moisture, in the absence of the application of special heat and light, will move from one sheet to the other to a greater extent in the non-image areas than in the image areas.

In a first of several variants of the developer embodiment, an impermeable base sheet is provided with a thin porous film which contains moisture and a reacting chemical (developer reactant). The treated surface of the copy sheet is then held against a printed surface for a sufiicient time to permit the selective vapor diffusion of moisture to take place, thereby resulting in the drying out of the nonimage areas while the image areas remain moist. The copy sheet is developed by exposing the film to a developer such that the developer permeates the moist image areas to react with the developer reactant. The preferential permeation and reaction of the developer with the developer reactant in the moist image areas brings out the image.

This form of the developer embodiment is demonstrated most easily by forming a porous film on a transparent impermeable base sheet to form a copy sheet. The porous film is sensitized by moistening it with an aqueous solution of an acidic material such as salicylic acid. The moistened film is held against a printed cellulosic sheet until the moisture underlying the non-image areas of the printed sheet selectively `migrates into the printed sheet leaving the areas of the film overlying the image areas of the printed sheet in a moist condition. The copy sheet is then subjected to a developer which is a color-forming substance which reacts with the acidic material, the developer being contained in an inert liquid carrier. The reaction will take place in those moist areas which permit the colorforming substance to permeate the porous film and react `with the acidic material in the film.

In a second variant which eliminates any need for handling solutions which might harm documents or per sonnel, the copy sheet is prepared by forming a porous film containing a developer reactant on the surface of an impermeable base sheet. According to this procedure, suitable inorganic porous films containing water-insoluble acids are formed on the surface of an impermeable base. These films can be prepared, for example, by baking acid clay slurries of bentonite or kaolin and the like onto glass, aluminum and the like.

Alternatively, the acidic inorganic compounds can be bonded with conventional adhesives to any suitable base. The copy sheets can then be moistened and exposed to printed surfaces, as above described, and subsequently subjected to a developer which reacts in the moist areas with the acidic material in the porous film to form a visible image.

Similarly, organic acidic polymers can be employed to form the porous film on an impermeable base. Acidic polymers, such as those offered for use as ion-exchange, thickening agents, alkali-dispersed adhesives and the like are suitable.

A third variant for providing an impermeable base shee-t with a porous film which contains moisture and a reacting chemical (developer reactant) is within the purview of this form of the developer embodiment. According to this procedure, a surface of a suitable impermeable film such as cellulose acetate, cellulose nitrate and the like, is

swelled or porosified by treatment with a solution of developer reactant such as phosphoric acid or acetic acid, salicyclic acid and the like. The film is then subjected to controlled rinsing time with Water so as to leave the necessary concentration of acidity and blotted free of excess water to obtain a moist, acidcontaining porous film on an impermeable base. This can be developed according to the procedures discussed above.

In a fourth variant of the developer embodiment, an extremely thin porous film on an impervious base sheet is moistened with a liquid, such as water alone, and applied to a printed sheet. The sheets are held together until the selective vapor diffusion takes place, causing the copy sheet to become relatively dry in the non-image areas while remaining moist in the image areas. The copy sheet is immediately subjected to a developer constituted by a substance or combination of substances which reacts in the presence of moisture but does not react in the absence of moisture to bring out the image. For example, an acidic while remaining moist in the image areas. The copy sheet is immediately subjected to a developer constituted by a substance or combination of substances which reacts in the presence of moisture `but does not react in the absence of moisture to bring out the image. For example, an acidic reactant such as salicylic acid, and a color former, such as a leuco base of an auramine dye (Color precursor #l by Allied Chemical Corp.) as disclosed in Pat. No. 2,981,- 733 and further discussed in Pat. No. 3,079,271 can be dispersed or dissolved in an inert carrier liquid as, for example, toluene. The reaction between the acid and colorformer which takes place in the presence of water moisture brings out a purple-dyed image on the copy sheet.

The particular substances which are employed in the development of images on the copy sheet, according to t-he developer embodiment admit of considerably variation. For example, in the first variant of the developer embodiment in which the porous film of the copy sheet contains an image of moisture and a reacting chemical (developer reactant), the developer medium will contain any chemical, preferably a colorforming material, which 1will react with the developer reactant in the moist image areas to produce a visible image. As such, the developer will depend upon the type of developer reactant which is used. In one of the more easily operated forms of the invention, the developer reactant contained in the porous surface film is an acidic compound such as a salicylic acid, acetic acid, phosphoric acid, phthalic anhydride, formic acid, citric acid or acid salts such as sodium dichromate, sodium bisulfites, acid sulfates, aluminum sulfate, aluminum chloride, ferric chloride and the like. Alkaline materials can be substituted for the acidic materials and include calcium hydroxide, sodium carbonate, sodium acetate, potassium citrate and alkali borates. Any of a number of color-forrning substances can be employed as a developer with these basic and acidic developer reactants, including a leuco base of an auramine dye (Color precursor #l by Allied Chemical Corporation) and the like. It is, of course, obvious that the substances listed under developer reactants can be employed as developers and vice versa. The adoption of these terms is merely to designate the location of reacting substances (ie.) developer reactant signifying the substance on the porous film which will be reacted with a developer applied to the film after the film has undergone the vapor diffusion step upon contact with the printed sheet.

In the fourth variant of the developer embodiment in which the porous film of the copy sheet is moistened with water alone, the developer medium will contain a substance or combination of substances which react in the presence of the moisture but not in the absence thereof. As described above, a suitable developer medium would be a rnixture of an acidic material such as salicylic acid and Color precursor #1 dispersed in toluene which reacts in the presence of the moist-water image to form a purpledyed image on the surface of the copy sheet. While a 1 1 chemical reaction in the presence of moisture is desirable, since it permits using essentially colorless, not-straining solutions, it is not essential. For example, a dye may be dissolved in a suitable solvent which will stain the moist (or dry) areas to form an image.

It is preferred to dissolve or disperse the developer in an inert carrier liquid. In such form, the developer should -be appreciably soluble in the moist image areas as well as in the inert carrier liquid, so as to permit diffusion of the developer into the moist image areas to react `with the developer reactant. When only a moist image, such as water moisture alone, has been formed in the absence of a developer reactant, the developer will react in the presence of the moist image to stain or dye the copy sheet. The iner-t carrier for the developer should have almost no solubility in the moist image or otherwise it will absorb the pattern of moisture on the film before the image forms. Suitable inert carrier liquids include aliphatic and aromatic hydrocarbons such as kerosene, white oil benzene, toluene and other petroleum hydrocarbons; substituted hydrocarbons such as liquid halogenated hydrocarbons, including the Freons, such as l,l-dichlorotriuoroethane, 1,2- dibromo tetrauoroethane, 1,1,1 trichloropentafluoropropane, 1,2 difluoro tetrachloroethane perfluorodimethyl cyclobutane and the like; and halogenated aromatic hydrocarbons such as halogenated benzene, biphenyl and the like.

By subjecting them to a gaseous developer, development of the moist images can be accomplished, thus avoiding the need for supporting the developer in a liquid carrier. For example, when the developer reactant in the moist image areas formed by vapor diffusion is a color-former such as a leuco base of an auramine dye (Color precursor #l by Allied Chemical Corp.), the vapors of acidic developers such as hydrochloric acid, formic acid, acetic acid, chlorine and the like will react with it and form the colored image. Similarly, vapors of basic developers will react with a developer reactant on the surface of the copy sheet. For example, ammonia vapors will react with a copy sheet surface dyed-blue with mixture of salicyli(` acid and Color precursor #1 to bleach the dye in the moist image areas.

The base sheet of the copy sheet employed in the developer embodiment can be any impermeable material. Since the image imparted to the copy sheet surface will be a mirror reproduction of the printed surface, the base sheet is preferably transparent. The base sheet is preferably capable of being bonded to the porous surface lm so that the porous lm cannot easily be removed.

For example, the base sheet may be plastic, glass, rubber and the like. Suitable examples of the plastic material are polyvinyl chloride, polyesters (Mylar), polystyrene, polyethylene, vinyl-vinylidene chloride polymers (Saran), cellulosic polymers, polyacrylates and the like.

The porous film may be formed integrally with the base sheet as, for example, by subjecting cellulosic acetate to a solvent such as acetic acid to swell the surface of the base sheet and thereafter rinsing the acetic acid off the surface, thereby forming a porous discontinuous yfilm of cellulose acetate. Alternatively, the porous film may be formed by applying a coating to the base, the film being constituted by a thin layer of colloidal organic or inorganic material.

Examples of the suitable porous films are (l) regenerated cellulose (most easily produced in very thin layers by superiicially hydrolyzing cellulose nitrate, cellulose acetate-butyrate and the like); (2) organic colloids such as gelatinized polyvinyl alcohol, polyvinyl pyrrolidone, pectin, guar gum, casein, carboxy methyl cellulose, hydroxy ethyl cellulose, alginates, lignosulfonates and the like; (3) inorganic colloidal materials such as hydrolyzed ethyl silicate (and similar forms of polysilicic acid, colloidal silica or silica gel); hydrated oxides of alumina, iron, copper, zinc, zirconium, and the like; ferrocyanides; bentonite, kaolin and the like; (4) soaps and the surface- 12 active materials capable of forming micelles or coacervates which have suitable permeabilities.

The moisture medium which forms the image areas on the copy sheet by selective vapor diffusion to or from the non-image areas of the printed surface is preferably water, although it is possible that other solvents or solvent systems can be employed. As has been discussed, water alone or water containing a reacting chemical (developer reactant) can form the moist image areas. Water is preferred for several reasons including its low cost, its ability to be absorbed by cellulose to an extraordinary degree, its harmless effect on printed paper and personnel, and its freedom from any disturbing aroma.

The following examples will serve to illustrate the practice of the developer embodiment of this invention but are not to be considered as limitations thereof.

EXAMPLE 3 l A sheet of cellulose acetate was treated for ten minutes at room temperature with a bath conatining 100 ml. of dimethyl sulfoxide, 40 ml. of water, l0 grams of salicylic acid and 5 grams of dioctyl sodium sulfosuccinate. This treatment caused the surface of the cellulose acetate to swell. The cellulose acetate sheet was then rinsed in water for 5 seconds and then blotted free from excess liquid. The sheet, which had no liquid visible on its surface, was allowed to dry for 5 seconds to eliminate any stickiness and then it was placed in contact with a printed sheet of paper for seconds. The sheet was then removed from the printed paper and merely dipped in a 0.5 percent solution of a leuco base of an auramine dye (Color precursor #l by Allied Chemical Corporation) in kerosene. A deep blue positive image developed on the cellulose acetate copy sheet in about seconds, and was prevented from developing further by blotting off the excess kerosene. The image on the surface of the cellulose acetate copy sheet was sharp and legible in deep blue. This image on the surface corresponded to the mirror image of the printed matter on the paper and was right reading when viewed from the side of the copy sheet opposite the treated surface.

EXAMPLE 32 A copy sheet of polyethyleneterephthalate (Mylar) having a thin, porous film of gelatin was soaked in water, blotted free of excess liquid and allowed to dry for about seconds to eliminate any tendency to stickiness. The moist gelatin surface of the copy sheet was then held in uniform contact with a printed sheet of paper for about 10 seconds. During this period, water vapor diffused from the copy sheet in the unprinted areas of the paper while the copy sheet remained moist in the image areas. The copy sheet was then treated with a solution of toluene containing about 5% Color precursor #1 and about 2% salicylic acid. An intense purple image appeared on the copy sheet in the moist image areas.

EXAMPLE 33 A sheet of cellulose acetate was treated for 5 seconds at room temperature with a bath containing 100 ml. of dimethyl sulfoxide, 250 ml. of methanol, ml. of water, 1 grani of salicyclic acid', 5 grams of Color precursor #1. This solution swelled the surface of the cellulose acetate and at the same time dyed it blue. The dye-blue cellulose acetate copy sheet rinsed in Water for 10 seconds and blotted free of excess liquid. The copy sheet, which had no liquid visible on its surface, was allowed to dry for 5 seconds and then held in contact with a printed sheet of paper for about 15 seconds. The copy sheet was then immersed in a ml. kerosene solvent containing 20 ml. oleic acid and 5 ml. of 28% ammonia The ammonia was present in the kerosene solution in sufcient excess to give a distinctly alkaline reaction. The alkalinity destroyed the blue color of the film wherever it was moist with `Water which had not vapor diffused to the printed paper in the areas of the 13 printing. The resulting surface of the copy sheet contained an image of clear characters on a blue background Which when viewed from the opposite side of the sheet, read right.

EXAMPLE 34 A cellulose acetate sheet was dipped in a solu tion of a Color precursor #1 in dimethyl sulfoxide. for 5 seconds. It was then rinsed with water, blotted free of excess liquid and held in contact with a printed sheet of paper for a few seconds. After removal, the cellulose acetate copy sheet was exposed to the vapor of hydrochloric acid. A deep blue image developed on the copy sheet in the moist areas where the dye reacted with the hydrochloric acid.

The vapor development of the image on the copy sheet in the above example was also accomplished with formic acid and acetic acid vapors.

EXAMPLE 35 A glass plate was coated with a 2.5% aqueous solution of equal parts by weight of poly(vinylmethyl ethermaleic anhydride) and polyvinyl alcohol by flowing the solution on the plate and draining off the excess. The coated plate was dried in an oven at about 215 F. for one-half hour. Under these conditions, there was enough reaction between the poly(vinylmethyl ether-maleic anhydride) and polyvinyl alcohol to make the coated film insoluble in Water, but it would still swell. The coated -glass was then soaked in Water, blotted free of excess liquid and allowed to dry for a few seconds to eliminate stickiness. The moistened copy sheet was contacted with a sheet of printed paper for about 30 seconds and then dipped in a 1% solution of Color precursor #1 in kerosene. A deep blue image of characters appeared on the surface of the copy sheet.

EXAMPLE 36 A cellulose acetate copy sheet was dyed blue according to Example 33 and contacted with the printed sheet of paper according to the same procedures described therein. The image on the surface of the copy sheet was developed by exposure to ammonia vapor instead of the liquid development described in that example.

image of clear characters on a blue background was delveloped.

EXAMPLE 37 A glass plate was coated with a slurry of parts by weight of kaolin and 5 parts by weight of 85% phosphoric acid in about 80 parts by weight of water. The plate was dried and baked for about half an hour in an oven at about 400 F. This procedure bonds the clay to the glass so firmly that it will not rub off, even if held under running Water and scrubbed. The coated surface of glass was then dipped in water, after which it was placed between absorbent paper towels to blot off the excess liquid. The water moisture laden surface of the coated glass was then held in uniform contact with a printed sheet of paper for about 5 seconds and then dipped into a developer solution containing 1% Color precursor #1 in kerosene. After the sheet was removed from the developer solution, a permanent blue image appeared on the surface.

lMAGE TRANSFER EMBODIMENT In the foregoing selective diffusion and developer processes, an image is formed on the copy sheet by what can be considered a one step process insofar as the transfer of an image from one sheet to another is conce1-ned. The one step transfer necessarily results in a mirror image on the copy sheet. The mirror image, to be read, requires the use of a transparent copy sheet and the reading of the image through the .reverse side of the copy sheet. The use of the transparent copy sheet is perfectly satisfactory from the standpoint of obtaining a useful, readable, and permanent copy of the printed page but is not as easy to handle as paper formed of cellulose fibers.

The objective of the instant transfer embodiment of the invention is to provide a process for making rightreading images on paper. This embodiment is a two step process in Which the mirror image is first made by the selective diffusion of vapor and thereafter the image is transferred to paper.

More specifically, in the image transfer process, a copy sheet is prepared by forming an extremely thin porous film on one surface of an impermeable sheet and moistening the film as described in the previous embodiments. The moistened film is held against a printed sheet until a mirror image is reproduced in the film through the selective drying of the film in the non-image areas. The image thus formed in the remaining moist areas may be transferred to a paper final sheet in one of two ways. ln the first of these, the copy sheet is subjected to a liquid developer as described in Example 3l, for instance. Immediately following the application of the developer, the copy sheet is wet with the developer solution, the image areas being Wet with the dye by which the readable image is formed. While wet, the copy sheet is placed with its Wet film side against a paper final sheet until enough of the wet dye in the image areas flows from the copy sheet to the final sheet to reproduce the image on the final sheet. This form of the transfer embodiment requires the use of the liquid developer but, nevertheless, is effective in producing a legible reproduction on paper.

The second form of this embodiment of the invention is preferred in that it does not require the use of a liquid developer. This form of the invention utilizes a final sheet having a specially prepared coating and a copy sheet whose porous film is moistened with a specially prepared liquid which will combine with the final sheet coating to bring out an image. More particularly, the copy sheet has its porous film moistened with the special liquid and the copy sheet is placed against the printed sheet. The film is dried out in the non-image areas through the selective vapor diffusion and the copy sheet is placed with the film surface against the specially coated film paper. The moisture in the remaining image areas diffuses as a vapor into the coating of the final sheet and combines with that coating to bring out a legible, right-reading image.

In this second form, only the image formed in the last step need be permanent. Therefore, the copy sheet can be made more durable than is contemplated for the embodiments described earlier, for the porous film may be remoistened and reused as often as desired.

This form of the transfer embodiment admits of the marketing of a unit containing three items, namely, a package of paper having a suitable coating, a plate having a microporous film (copy sheet), and means for applying a sensitizing solution to the plate. The paper and copy plate would normally be maintained in an unsensitized condition so that the materials could be stored indefinitely. In use, it is merely necessary to moisten the microporous plate using the means provided therefor, to place the moistened plate in contact with the printing to be copied for a sufficient length of time to effect the selective migration of the sensitizing vapor, and then to contact the plate with the specially coated paper. The microporous film on the plate, therefore, can be of a very durable material such as unglazed porcelain, microporous glass, sintered stainless steel, or a very tough plastic of suitable porosity. Its durability admits of moistening by rubbing it over an applicator such as a sponge, pad, ringer, or squeegee.

The second form of the transfer embodiment admits of a number of variants which will be described in more detail in the examples set forth below.

A first of these variants is in a sense an extension of the selective dissolution embodiment. In accordance with this variant, an impermeable copy sheet having a very thin porous film is sensitized with a mixture of a solvent and a carrier liquid, preferably water. The porous film does not necessarily have to be solvated in the solvent unless it is desired to make a permanent wrong-reading image as well as a transferred right-reading image. The final sheet, however, must have a thin film capable of being solvated by the solvent and having its optical properties altered by the dissolution.

In the practice of the process, the sensitized copy sheet is placed against a printed sheet and the water selectively diffuses into the printed sheet to a greater extent in the non-image areas than in the image areas until the solvent becomes concentrated to the degree necessary to solvate the film on the final sheet. Thereupon, the copy sheet is placed against the film of the final sheet for a few seconds. During this time, the concentrated solvent in the non-image areas vaporizes and migrates to the adjacent film areas of the final sheet and solvates the film to change its optical properties. In the image areas, the concentration of the solvent is not changed to any appreciable degree during the application of the copy sheet to the printed sheet and, hence, the migration of the vapors of the mixture into contact with the film of the final sheet has no appreciable effect on the optical properties of the film in the image areas. Thus, a permanent image is created.

A second variant is similar to the first in respect to the structure of the final sheet. The copy sheet preferably is constituted by an impermeable base having a thin, porous film of a relatively inert material such as clay, porcelain, or the like. In contrast to the first variant, the sensitizing medium may be a pure solvent or may be a solvent initially concentrated to the degree necessary to solvate the film on the final sheet.

The copy sheet is placed against the printed sheet and a selective migration of the solvent occurs as between the image areas and non-image areas, the image areas forming a barrier to the migration of the solvent. The copy sheet is held against the printed sheet until the vaporization and migration has proceeded `to the extent necessary to achieve a drying out of the copy sheet film in the non-image areas. The copy sheet is then placed against the film of the final sheet. In the image areas, the solvent vaporizes and migrates to the film of the final sheet and solvates it to alter its optical properties. In the non-image areas, however, the copy sheet film is dry or at least relatively dry to the extent that any vaporization and migration of vapor of the solvent is insufiicient to have lany marked effect on the film of the final sheet.

The second variant is distinguished from the first principally in the fact that there is no reliance placed upon the selective acceptance of a carrier liquid (water) by the cellulose of the printed sheet t increase the concentration of the solvent of the sensitizing mixture.

In a third variant, the final sheet has on one of its surfaces a first coating of a dye, preferably oil soluble, and a top or final coating or skin which is thin but covers the dye. The top coating can, for example, be a standard pigment and binder such as is well known in the coating of paper. It is preferred that the dye be oil soluble so that it is not affected by the application of the cover coating which normally is applied as an aqueous dispersion and so that it will not be affected by conditions of high humidity.

The copy sheet is constituted as in the first embodiment and is sensitized by a solvent for the dye. The copy sheet is held against a printed sheet until the solvent vaporizes and migrates toward the printed sheet to the extent that in the non-image areas of the copy sheet the solvent is substantially depleted. In the image areas, the barrier formed by the printed images prevents the depletion of 16 the solvent. The copy sheet is then placed on the final sheet and the solvent remaining in the image areas vaporizes and migrates through the porous cover layer into contact with the dye on the final sheet. The dye dissolves through the contact with the solvent and diffuses through the cover layer and causes a visible stain corresponding to the image reproduced.

In the fourth variant, the final sheet contains a dye former. The dye former can be applied by introducing it as a part of the tub-size, as a part of a final coating or by painting it onto the surface of the paper. The copy sheet is formed as in the previous variants and sensitized with a solution of a substance which will react with the dye former. The copy sheet is applied to a printed sheet until the areas overlying the non-image areas of the printed sheet become relatively dry while the areas overlying the image areas remain relatively moist. The copy sheet is then applied to the final sheet and the reacting substance in the moist image area migrates into the final sheet and reacts with the dye former to bring out an image in the final sheet.

A fifth variant is similar to the second variant except that the mechanism for bringing out the image is the opposite of that of the second variant. It is formed by coating a clear lacquer on a dark substrate. The copy sheet is sensitized with a liquid which will solvate the lacquer, as, for example, alcohol and water. The copy sheet is held against a printed sheet until the area overlying the non-image area becomes relatively dry with the area overlying the image area remaining moist. The copy sheet is then placed against the final sheet and the sensitizing liquid in the image areas vaporizes and moves into contact with the lacquer, causing it to swell and to appear white against the dark background.

In a sixth variant, image transfer is effected by physically pulling a coating away from either the copy sheet or the final sheet to form an image. For example, the copy sheet may be provided with a film which will adhere to a specially prepared surface of a final sheet when it is moist. The film of the copy sheet is moistened and placed against the printed sheet until the area overlying the non-image areas of the printed sheet becomes dry and the copy sheet is then placed against the final sheet so that the remaining moist image areas adhere to the final sheet then remain on the nal sheet when the copy sheet is pulled away. The film on the copy sheet could be colored and the final sheet white so that a positive colored image, would appear on a white background. The principle can be used by preparing films for the copy sheet and final sheet in which only the dry areas of the copy sheet will adhere to the final sheet, the result following transfer being a right reading negative.

Alternatively, the process can be reversed by providing the final sheet with a separable film which adheres tol the copy sheet only in either wet or dry areas, depending upon the constitution of the respective films of the copy and final sheets.

Obviously, the transferred coating may be black white, or colored and may include a dye or oleaginous material to form a spirit duplicating or lithographie master. Similarly, if one of the sheets from which the coating is removed is formed froml a porous base, the sheet could be used as a mimeograph stencil.

In a seventh variant of the transfer embodiment, an image is brought out by selectively dispersing a dye as by causing it to diffuse or migrate into a film upon which it is supported by creating a condition in that film which will cause the selective. migration. More specifically, if a base sheet is coated with a dye receptive film such as gelatin, polyvinyl alcohol, or polyvinyl pyrrolidone and recoated with a relatively concentrated solution of dye, preferably in a solvent which does not appreciably swell the base before the solvent evaporates, then this dye covered surface can have its optical properties changed by subjecting it, in its image areas, for example, to water 1 7 or other liquid which will swell the film, thereby per mitting the dye to diffuse into the film.

In a species of this variant of the invention, it is possible to subject an undyed film to a vapor which will change its permeability in the image areas and thereafter to fiow a dye across the film, permitting the dye to diffuse selectively into the film only in the image or nonimage areas. This approach is less attractive than the approach wherein the film is initially dyed in that it requires the application of a liquid dye after the image is first obtained on a copy sheet.

Thus, in the preferred form, a final sheet would be prepared as described by applying a dye receptive film to any suitable base sheet and applying a dye to the film. A copy sheet is formed as previously described by forming a very thin porous film on an impermeable base sheet (see Example 38(C) The film is moistened with water or other suitable liquid and is applied to a printed sheet for a sufiic-ient length of time to permit the liquid to vaporize and diffuse into the printed sheet in the nonimage areas and to leave, in the areas overlying the printed image, a moistened condition in the film. The copy sheet is then applied to the` final sheet and the moisture in the image areas migrates to the dye supporting film of the final sheet, which permits the dye to disperse into the film, thereby changing the optical properties of the surface of the final sheet only in the image areas.

EXAMPLE 38 (A) A polystyrene sheet was coated with a one percent solution of two parts by Weight of polyvinyl acetate and one part by Weight of Gantrez AN119 by General Aniline and Film Corp., i.e., poly(vinylmethyl ether-maleic anhydride) in acetone and dried to an opaque surface. This procedure produced a final sheet.

(B) A solution was prepared by mixing 3 grams of cellulose acetate-butyrate, 0.75 gram of Carbopol 934 in 30 rnl. of methyl acetone, 90 ml. of methanol and 60ml. of acetone. This solution was applied to one surface of a polypropylene sheet by dip-coating the sheet in the solution. The coated sheet was dried to a ground-glass, opaque surface.

The coated polypropylene sheet was then dipped in a sensitizing solution of 5 percent by volume each of propylene carbonate and isopropanol in 90% by volume of water. The sensitized copy sheet, after blotting off the excess liquid, was exposed to a printed sheet of paper for about l5 seconds. After removal of the copy sheet from the printed paper, it was then held in uniform contact against the fina] sheet prepared according to the procedure in (A) above. A right readable image was left on the final sheet.

(C) A glass plate was coated with a slurry of l parts by Weight of kaolin and parts by weight of 85% phosphoric acid in about 80 parts by weight of Water.

The plate was dried and baked at 400 F. for about onehalf hour to form an adherent porous coating.

The coated plate was Washed Well to remove free phosphoric acid and then treated with a sensitizing solution of 5% by volume each propylene carbonate and isopropanol in 90% water. After blotting off the excess liquid, the sensitized plate was exposed to a printed sheet of paper for about l0 seconds. After removal, the glass plate was held against the final sheet prepared in (A) above. A right readable image was left on the final sheet.

In practicing the steps of the process set forth in paragraphs (B) and (C), I have found that in some instances the optical properties of the non-image areas of the final sheet will be changed to provide a positive right-reading image, and, in other instances, the optical properties of the image areas will be changed to provide a negative right-reading image in the final sheet. In the latter instances, the sensitizing solution applied to the copy sheet apparently has been dried, in applying it to the printed surface, to the extent that there was insufficient sensitizing solution remaining in the non-image areas to affect the optical properties of the film of the final sheet in the last step of the process. The solvent overlying the image areas, however, became concentrated to the extent necessary tochange the optical properties of the final sheet and was present in sufficient quantity to do so. It should be noted that the selective absorption of the organic vapor by the coating on the final sheet may be a decisive factor, that is, the coating on the final sheet is an organoflic system which Will preferentially absorb the organic solvent vapors.

While the factors which determine the creation of a positive or a negative right-reading image in the final sheet are not clearly understood, it appears that the thickness of the copy sheet film, its porosity, the thickness of the final sheet film and its porosity, the relative evaporation rates of the solvent and water, the pressure and contact times during which the copy sheet is applied to the printed sheet and the copy sheet is applied to the final sheet, and the ambient temperature are all factors which will contribute to the selective creation of a positive image or a negative image in the final sheet.

EXAMPLE 39 A glass plate copy sheet was formed in accordance with the procedure set forth in Example 38(C). When this coating was moistened with a 20% aqueous solution of dimethyl sulfoxide, the excess liquid removed, and the surface pressed against a printed page, a negative image could be observed on the clay coated surface. This was transferred to a film coated with four parts by weight of polyvinyl acetate to one part by weight Gantrez AN119 (as formed in Example 38(A) to form a right-reading negative image in the film of the final sheet. The dimethyl sulfoxide was at the time of the application of the copy sheet to the printed sheet of sufiicient concentration to affect the optical properties of the film on the final sheet.

EXAMPLE 40 One-half gram of methylene blue and 5 grams of gelation were dissolved in 50 cc. of Water and 50 cc. of denatured alcohol. This solution, flowed on a piece of glass, dried to a deep blue color. A polypropylene base sheet which had been coated with 2 parts by weight of Gantrez AN119 and 3 parts by weight ethyl cellulose was dipped in a 10% aqueous solution of sodium dichlorocyanurate for 20 seconds, blotted free of excess liquid, placed in contact with a printed surface for l0 seconds, and thereafter held in contact With the blue gelatin surface for 10 seconds. A clear, negative image developed, colorless on a blue background. Similar negative images `were made by dipping the coated polypropylene sheet in 15% aqueous butyrolactone or in 5% propylene carbonate and 5% isopropanol and Water, these copy sheets being applied to the printed sheet and final sheet as described.

EXAMPLE 41 As an example of the fifth variant, a final sheet was prepared by coating polypropylene with a mixture of .375 gram Carbopol 934, four grams nitro cellulose, four grams resinous plasticizer (Santolite MHP-by Monsanto) dissolved in 60 cc. methanol, 60 cc. acetone, and 90 cc. ethanol and dried to a translucent coating.

A copy sheet was formed by coating a glass plate with a kaolin film as provided in Example 38(C). The copy sheet was sensitized by moistening it with a mixture of cc. denatured alcohol, 120 cc. water, and one cc. ammonia (28%). The copy sheet Was applied to a printed sheet for a sufficient length of time to dry out the areas of the film overlying the non-image areas of the printed sheet while the image areas remained moistened. The copy sheet was then applied to the film of the final sheet until the sensitizing moisture migrated into the film of the final sheet to bring out a white image in the areas in which the moisture migration took place.

19 The process was also performed using only water to sensitize the film of the copy sheet and a recognizable image was obtained.

EXAMPLE 42 Image formation by the sixth or adhesive variant involves the possibility of having the adhesive surface so sticky that it adheres to the printed page. To avoid this, it is preferable to form the primary image on a copy sheet coating which when wet is mechanically weak but nonsticky and to press it against a final sheet surface which becomes sticky at high moisture content. More specifically, a copy sheet was formed by coating a sheet of polypropylene with a 9% solution in methanol of approximately equal parts by weight of nitro cellulose and Santolite MHP. The final sheet was formed by coating polypylene Carbopol 934 and enough red dye to provide a distinct color. The copy sheet film was moistened with water and placed against a printed sheet for a sufficient length of time to dry out the areas of the film overlying the non-image areas of the printed sheet while the image areas remained moistened. Thereafter, the copy sheet was pressed against the film of the final sheet. The Water in the image areas migrated to the Carbopol film which became sticky due to the presence of the moisture and adhered to the copy sheet. When the copy sheet was removed, portions of its lm corresponding to the image areas remained on the sticky surface of the final sheet, thereby providing a white image on the red background of the final sheet.

EXAMPLE 43 As an example of the seventh variant, a glass plate was coated with gelatin. The gelatin was dried and was then flowed with a solution of an intense dye such as one gram of Du Pont Victoria Green in 100 cc. of toluene and 100 cc. ethylene glycol monoethyl ether. When the solvent evaporated, a uniform bronze overtone was left over a pale green background. A copy sheet was Ormed by coating a glass plate with a kaolin film as described in Example 38(C). The film of the glass plate was moistened with water and applied to a printed sheet for a sufficient length of time to dry out the non-image areas overlying the printed image to leave the image :areas in a moist condition. The copy sheet was then placed against the dyed final sheet until the moisture in the image areas of the copy sheet migrated into the final sheet, causing the final sheet film to swell and the dye to disperse into the swollen film, thereby bringing out a right-reading image.

What is claimed is:

1. In the process of reproducing an image from a printed sheet to an impermeable copy sheet having a solid porous surface capable of retaining moisture, the printed sheet having image areas which have an avidity for moisture different from the non-image areas, the steps of,

moistening said copy sheet surface, and

placing said copy sheet surface on said printed sheet for a sufficient length of time to permit said moisture to diffuse from the copy sheet to the drier printed sheet selectively to the greatest extent in the unprinted areas thereby reproducing in the copy sheet surface an image corresponding to the printed sheet image.

2. In the process of making copies from a printed sheet whose image areas have an avidity for moisture different from the non-image areas, the steps of,

providing an impermeable copy sheet having a thin porous solid film on its surface,

moistening said film, and

holding said copy sheet with said moistened film in contact with said printed sheet until substantial moisture diffusion occurs from said copy sheet to the drier printed sheet selectively ot the greatest extent in the unprinted areas thereby reproducing in the 2,0 copy sheet an image corresponding to the printed sheet image.

3. The process of claim 2 wherein said printed sheet comprises a printed cellulosic sheet whose image areas are printed with an ink forming a barrier to the migration of said moisture from said copy sheet.

4. The process of claim 2 wherein said moisture diffuses as a vapor from said copy sheet to said drier printed sheet.

5. The process of claim 2 wherein said diffusion is conducted in the absence of special light and heat.

6. The process of reproducing an image from a printed sheet to an impermeable copy sheet having a solid porous surface capable of retaining moisture, the printed sheet having image areas which have an avidity for moisture different from the non-image areas comprising the steps of,

moistening said copy sheet surface,

placing said copy sheet surface on said printed sheet for a sufficient length of time to permit said moisture ot diffuse from the copy sheet surface to the drier printed sheet selectively to the greatest eX- tent in the non-image areas, and

developing the areas of said copy sheet surface having the greatest remaining moisture.

7. The process of reproducing an image from a printed sheet of cellulosic fibers whose image areas are printed with an ink which forms a barrier to migration of moisture comprising the steps of,

providing an impermeable copy sheet having a thin porous solid film on its surface,

moistening said film with a liquid constituted at least by water,

placing said copy sheet on said printed surface for a sufficient length of time for the moisture selectively to diffuse from the film to the non-image areas of said printed sheet, and

subjecting said copy sheet to a developer which combines with said li-quid in the surface of said film in the areas of greater remaining moisture content to produce a visible image.

8. The process of claim 7 wherein said moisture diffuses as a vapor from said film to said printed sheet.

9. The process of claim 7 wherein said liquid is water alone.

10. The process of claim 9 wherein said developer comprises a liquid mixture of an inert carrier and two substances consisting essentially of a color-former and a developer reactant which react with each other in the presence of said water in said areas of greater remaining moisture content.

11. The process of claim 7 wherein the process further comprises, as a nal step, pressing said copy sheet against a final sheet to transfer said moist visible image from said film to said final sheet.

12. The process of reproducing an image from a printed sheet of cellulosic fibers whose image areas are printed with an ink which forms a barrier to migration of moisture comprising the steps of,

providing an impermeable copy sheet having a thin porous solid film containing a developer reactant on its surface,

moistening said film with water,

placing said copy sheet on said printed surface for a suficient length of time for moisture selectively to diffuse from the film to the non-image areas of said printed sheet, and

subjecting said copy sheet to a developer which reacts with said developer reactant in the surface of said film in the areas of greater'remaining moisture content to produce a visible image.

13. The process of reproducing an image from a printed sheet of cellulosic fibers whose image areas are printed with an ink which forms a barrier to the migration of moisture comprising the steps of,

providing an impermeable copy sheet having a thin porous solid lm on its surface,

moistening said `film with an aqueous solution of a developer reactant, placing said copy sheet on said printed sheet for a sufiicient length of time for the moisture of said solution selectively to diffuse from the film to the non-image areas of said printed sheet, and

subjecting said copy sheet to a developer which reacts with said developer reactant to produce a color, said developer permeating said copy sheet and reacting with said developer reactant in the areas of greater remaining moisture content to produce a visible image.

14. The process of claim 13- wherein said aqueous solution of developer reactant is acidic.

15. The process of claim 13 wherein said developer comprises vapors of a substance which reacts with said developer reactant to produce said color.

16. The process of claim 13 wherein said developer is homogeneously contained in an inert liquid carrier.

17. The process of reproducing an image from a printed surface comprising the steps of,

providing an impermeable copy sheet having a thin porous solid iilm on its surface, moistening said film with a liquid capable of producing a visible image on a final sheet,

placing said copy sheet on said printed sheet for a suicient length of time for the moisture of said liquid selectively to diffuse from the lm to the nonimage areas of said printed sheet, and

pressing said copy sheet against the final sheet to transfer the remaining liquid to said iinal sheet to form a Ivisible image on the iinal sheet.

18. The process of claim 17 wherein said moisture diffuses as a vapor from said lm to said printed sheet.

19. The process of claim 17 wherein said tinal sheet has a layer capable of having its optical properties changed due to a transparentization or opacification by the presence of said remaining liquid to produce said visible image in said inal sheet.

20. The process of claim 17 wherein said iinal sheet has a layer of a dye receptive material and a dye covering said dye receptive material, said remaining liquid being transferred to said iinal sheet layer in the image areas and causing said dye to disperse into said dye receptive material to produce said visible image in said final sheet.

21. The process of reproducing an image from a printed sheet of cellulosic iibers whose image areas are printed with an ink which forms a barrier to migration of moisture comprising the steps of,

providing an impermeable copy sheet ha-ving a thin porous solid iilm on its surface,

moistening said film with a liquid capable of diffusing in the absence of special heat and light,

providing a nal sheet having a layer of a substance capable of reacting with said liquid to form a visible image,

placing said copy sheet on said printed sheet for a suf- Iicient length of time for said liquid to diffuse in the absence of special heat and light selectively from the film to the non-image areas of said printed sheet, and

placing said copy sheet on said iinal sheet for a sufficient length of time for said liquid remaining in the image areas of said copy sheet to contact said substance on said final sheet, thereby forming a right reading image on said iinal sheet.

22. The process of claim 21 wherein said iinal sheet layer comprises a dye soluble in said liquid, and a permeable skin covering said dye, and said right reading image is formed on said final sheet by said liquid remaining in the image areas of said copy sheet contacting the dye on said iinal sheet to dissolve it vwhereby said dye penetrates and stains said skin.

23. The process of claim 21 wherein said final sheet layer comprises a dye former and said right reading image is formed on said iinal sheet by said liquid remaining in the image areas of said copy sheet reacting with the dye former of said final sheet.

24. The process of making copies from a printed sheet comprising the steps of,

providing an impermeable base sheet having a very thin opaque solid iilm of a substance which will retain the moisture of a sensitizing liquid and Whose optical properties can he permanently altered by diffusion of said sensitizing liquid,

moistening said films with said sensitizing liquid,

holding said base sheet with said moistened film against said printed sheet for a time sufficient for the moisture of said sensitizing liquid to diffuse from said film toward said printed sheet to a greater extent in the unprinted areas of said printed sheet, and

thereafter removing said base sheet from said printed sheet,

whereby a permanent mirror image is reproduced in said film due to a change in the optical properties by transparentizingor opacifying said iilm.

25. The process according to claim 24 wherein said liquid comprises a mixture of water and an organic solvent.

26. The process according to claim 24 wherein said printed sheet is a printed cellulosic sheet whose printing forms a barrier to the diffusion of said moisture.

27. The process according to claim 26 wherein said liquid comprises a mixture of Water and an organic solvent.

28. The process of claim 24 wherein said diffusion is conducted in the absence of special light and heat.

29. The process of claim 24 twherein said printed sheet comprises a printed cellulosic sheet whose printing forms a barrier to the migration of moisture and said impermeable base sheet is transparent.

30. The process of claim 24 wherein said moisture diffuses as a vapor from said lilm to said printed sheet.

31. The process according to claim 29 wherein said hlm is formed on said base sheet and moistened by subjecting an impermeable solvent sWellable transparent copy sheet to an organic solvent to swell the surface of said sheet, and

rinsing the swollen surface of said copy sheet with water until the solvating action ceases and the concentration of said solvent is reduced to the extent that it is too weak to further aiiect said copy sheet, thereby providing a thin opaque porous ilm containing a mixture of water and said solvent.

32. The process according to claim 29 wherein said iilm is formed on said base sheet and moistened by subjecting an impermeable transparent sheet to a solvent for said sheet and rinsing said solvent with water to form a thin opaque porous iilm on its surface, and

moistening said film with a mixture of water and an organic solvent.

33. The process according to claim 32 wherein said impermeable transparent sheet is cellulose acetate.

34. The process according to claim 33 wherein said solvent is dioxane.

35. A copy sheet package comprising,

a copy sheet constituted by an impermeable base sheet selected from the group consisting of plastic, glass and elastomeric materials and a thin porous solid film having a thickness in the range of 0.01 mil to 0.5 mil on at least one surface of said base sheet,

a sensitizing liquid absorbed in said porous film, said sensitized copy sheet capable of copying an original printed sheet in the absence of special heat and light,

a sealing sheet overlying the porous film of said copy sheet and extending a substantial distance beyond the peripheral edge of said copy sheet, and

a bottom sealing sheet covering the base sheet of the copy sheet and extending a substantial distance beyond the peripheral edge of said copy sheet, said sealing sheets being sealed together in a continuous seal extending around the extending portions of said sealing sheets, said film being capable of having its optical properties changed upon diffusion of said liquid to the printed sheet so as to reproduce the printing on said copy sheet, said sealing sheet overlying the porous lm being removable from said copy sheet lm for exposure of said lm to said printed sheet.

36. A copy sheet package comprising,

a copy sheet constituted by an impermeable base sheet selected from the group consisting of plastic, glass and elastomeric materials and a thin porous solid lm having a thickness in the range of 0.01 mil to 0.5 mil on at least one surface of said base sheet,

a sensitizing liquid absorbed in said porous film, said lm beingicapable of having its optical properties changed upon diffusion of said liquid in the absence of special light and heat to a printed sheet so as to reproduce the printing on said copy sheet, said copy sheet in a sealed container for maintaining the copy sheet in its sensitized condition for immediate copying application to said printed sheet.

37. The copy sheet package of claim 36 wherein said said film is opaque and is formed on one surface of said base sheet.

References Cited UNITED STATES PATENTS Dalton 1l7-36.7

Workman 11736.7 X

Dodge 161-1 Payne 118-269 Ball 41--21 Berguin 117-144 X Starck l17-138.8 X Mahler 117--138.8 X Maso et al. 206--54 Parlour 117-144 X Picard 118-624 X Walkup 117-175 X Gold et al. 11736.7 X Clark et al. Z50- 65.1 X

FOREIGN PATENTS WILLIAM D, MARTIN, Primary Examiner E. J. CABIC, Assistant Examiner U.S. C1. X.R. 

